1. Field of the Invention
The present invention relates to an image forming method in which an electrostatic image on an electrophotographic photoreceptor is developed by a developer containing a toner and the developed image is transferred onto a transfer medium such as paper and fixed to form the image.
2. Related Art
In early cases, full color image forming methods by the electrophotography are mostly utilized for businesses of color photo copying and designer. Recently, however, a composite color printing machine usable either for color printer or color copier is frequently introduced into offices. It is the background of such the trend that the coast lowering, miniaturization and speedup of the machine are progressed and that a business document such as a planning paper and a report can be output by the composite color printing machine connected with a personal computer through network accompanied with the introduction of information technology into the office.
An “oil-less color machine” is sold on the market in which the trouble relating to oil, such as silicone oil, is dissolved by giving a parting property to the toner so that a high quality color image having an improved smoothness of the image surface after the fixing can be obtained, for example, Japanese Patent Tokkai Hei 9-120225 and Tokkai Hei 9-197882.
Though a color toner image inhibited in the glossiness is proposed by the maker, a glossy image is strongly needed by the users accompanied with the spreading of the oil-less color printing machine. Moreover, the requirement level of the users for expanding the color gamut of the toner image is raised day by day so that the color reproduction with high fidelity can be realized.
As the measures for satisfying such the needs for the color image, a technique is proposed in which an oil-less toner containing a large amount of a low-melting point wax so as to smooth the surface of the toner image by the wax, and a technique is also proposed in which the viscosity of molten toner is reduced so that the mutual permeability of the toners of yellow, magenta and cyan is raised. However, the required level by the users cannot be satisfied.
The technique of the addition of a large amount of the wax is advantageous compared with usual crushed toner since a chemical toner typified by polymerized toner has a high degree of freedom of wax addition in the course of production. However, the technique for adding the wax to the toner has arrived to limits.
Moreover, it is confirmed that the exuding rate of the wax in the fixing process is difficultly controlled to suitable when the toner containing a large amount of the wax is employed. Namely, the wax cannot be constantly exuded while the fixing process since the wax is rapidly exuded at the initial stage of the fixation. As a result of that, unevenness of the glossiness is considerably formed on the surface of the toner image after the fixation. Particularly, in a recent high speed machine combined with an apparatus for post-treating the printed matter such as a finisher or a book binder, a problem is posed such as that the printed matter is partially touched with a conveying parts constituting the above apparatus so that the portion of the printed matter touched with the conveying parts is immediately cooled and difference in the glossiness between the portion rapidly cooled and that naturally cooled.
Furthermore, chance of outputting a lot of monochromatic images from a color printer is increased accompanied with speed up of the office use color printer. In other words, the monochromatic printer is not needed for printing the monochromatic prints because the high speed printing can be performed by the color printer. However, filming on the constituting parts of the printer tends to occur when a lot of the monochromatic documents with low toner consumption are frequently printed by the image forming method originally designed for color printer. When the toner containing a large amount of the low-melting point wax is introduced in such the case, the frequency of the problem occasion is raised and the life of the parts such as an intermediate transfer member, fixing member and photoreceptor is shortened so as to need exchanging of them on half way or renewing of the printer itself.
As above-mentioned, an image forming method in which the wax contained in the oil-less toner can be constantly exuded in the fixing process is demanded.